Hawaii Oceanic's below videos are of dolphins swimming who are using echolocation. Echolocation is a rapid clicking sound, where the dolphins use high frequency sound pulses that bounce off of objects in the water and refract back to the dolphin. The dolphin are able to interpret the returning sound waves and can "see" the object in greater detail through high frequency sound pulses than the dolphin could see if the dolphins' were relying upon their eyesight alone.

Dolphin can actually detect density differences in the object and can scan through fish, sand, and even people.

Sometimes you can even feel the buzzing if a dolphin is close enough to you and is echolocating your body.